Imaging devices, including charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) circuits, among others, have commonly been used in photo-imaging applications. A CMOS imager circuit includes a focal plane array of pixels, each one of the pixels including a photosensor, for example, a photogate, photoconductor or a photodiode for accumulating photo-generated charge in the specified portion of the substrate.
Pixels in an imaging device function to collect light relative to a portion of a scene or image being captured by the imaging device. Lenses may be used to enhance the collection of light at various levels of the image capture process by focusing incoming light onto specific light-collecting portions of the device, thereby decreasing the amount of light lost and increasing the fidelity of the captured image. Accordingly, a lens may be positioned above each pixel in a pixel array to focus incoming light on the photo-sensitive portion of the pixel. At a higher hardware level, an imaging device may further include one or more, larger lenses positioned above the entire pixel array.
In manufacturing lenses, the lenses may be created in a process which involves using a “lens master plate.” The lens master plate includes a plurality of lens shaped dies, which constitute “positive” lens shapes. A film is deposited over the wafer to create an intermediate “negative” of the lens master plate. The intermediate negative may then be used to create positive lenses for use in imaging devices. The negative may be formed for all lenses of all pixel arrays of an imaging device on a wafer.
One cost effective and efficient way to form a lens master plate having high-precision lens shaped dies is to obtain one or more single lens masters by, for example, precision diamond tuning, and replicating the master's lens shape through a step and repeat “stamp-and-step” method to populate an entire surface of the lens master plate. A common drawback of this method, as exercised in the current art on a contiguous film of polymer, is the effect the stamping of one lens die (“lens”) has on its neighbors. The stamping action displaces a certain amount of polymer, which can distort the shape of the neighboring lens. There is a need to minimize the variability in lens shape in lenses across an area of a lens master plate to be populated using the above described technique.